Of the 23 tracks that play host to races in NASCAR's premier series, 21 are owned by publicly traded companies such as International Speedway Corp. and Speedway Motorsports Inc. Officials with those tracks have said they don't provide attendance figures because they don't want to provide earnings guidance.

NASCAR regularly began including estimates with its race reports during the 2003 season. Calculating the figures is an inexact science at best because it includes several categories, such as grandstands, suites and the infield.

According to NASCAR estimates, 3,518,000 million attended last year's 36 Sprint Cup races. The average of 97,722 per event was the lowest since NASCAR began adding the crowd figures to race reports and down from a high of 4,670,400 (129,733 per race) in the 2005 season.